Antitrust charges must most immediately prove that a business acquisition is harmful to the consumer in some way. Given that Zuckerberg has assured Instagram users that this acquisition will not consolidate all of the app’s capacity to Facebook and that users will still be able to share photos on other social networks, that seems to preclude any harm that fans of Instagram would experience. However, there’s still some legwork to be done until Facebook becomes the official owner of Instagram.

As much of the coverage has glossed over the acquisition in such a way that it reads more like a how-to for purchasing used furniture off of craigslist, it’s not exactly that easy nor is the sale of Instagram a done-and-done deal yet. According to John Carney at CNBC, Facebook’s next step will be to submit a “Hart-Scott-Rodino filing” as part of a premerger notification program that “provides the Federal Trade Commission and the Department of Justice with information about large mergers and acquisitions before they occur.”

Carney’s sources tell him that the main roadblock that Facebook may encounter could be the price that Facebook offered Instagram. As the FTC has determined it, pricy acquisitions could suggest a deal will have anticompetitive effects. Given that speculation has begun to circulate that Zuckerberg’s hastened, non-board approved decision to purchase Instagram was more of a pre-emptive measure meant to act as a banana peel to slip up competitors, such a motivation could be interpreted as anticompetitive. That, of course, would likely give the FTC pause to approve of the deal if not outright deny it altogether. According to Dan Primack of Fortune, one source told him, “I think Facebook panicked, so it decided to take out the competition before it had a chance to grow even bigger.”

It’s no secret that Instagram had a handful of other potential suitors. Days before Facebook made its move, Instagram raised $50 million at a $500 million valuation from investors like Sequoia Capital. Even less of a secret is the known interest that Twitter’s Jack Dorsey had expressed in buying Instagram. Dorsey was even an early investor of Instagram, furthering the speculation that Facebook’s acquisition of the app was less about developing business and more about keeping Instagram out of Twitter’s hands. In March, Twitter acquired the upstart social blogging service Posterous so it’s understandable how the addition of Instagram to the Twitter armada could create a serious threat to the Facebook empire.

With at least two legitimate parties also interested in acquiring Instagram, Carney points out that if regulators at the FTC see any validity in those interests, the agency is likely to “scrutinize the deal a bit more closely.” However, that Facebook’s competition has previously picked up photography services – Google with Picasa and Yahoo! with Flickr – the social networking site does have some previous examples to cite should it start to feel the heat from the government.

While the approval given in previous instances of similar acquisitions bodes well for Facebook, there’s also the chance that a competitor could bring an action to the FTC even if the agency does approve of the deal. Even though Microsoft’s acquisition of Skype is nearly a year old, Cisco is still filing actions to the European Commission to prevent the deal on ground that the merger is in fact anticompetitive. Such an example illustrates that even if Facebook acquires FTC approval, it doesn’t necessarily mean that any would-be competitors are going to let the acquisition pass without a challenge.

You might recall previous business deals in the tech industry that didn’t receive the government’s blessing, such as last year’s saga of the failed AT&T/T-Mobile merger that the Justice Department blocked. Athough that decision eventually led to the proposed acquisition to completely unravel, it’d be difficult to argue that there are parallels between that merger and the Facebook/Instagram merger. The AT&T/T-Mobile deal involved two of the top four telecommunications companies in the United States. Facebook and Instagram are no where near being in a similar situation when it comes to comparing the social networking services.

It’s hard to say if any antitrust obstacles are likely to happen, let alone guaranteed. Where previous acquisitions were met with hesitation or outright denial by the powers that be, some have begun to question whether the FTC has begun to realize that these types of acquisitions aren’t quite as anticompetitive as they once seemed due to the constant and rabid growth of technology. That is, trends rise and fall so quickly in the tech world that it has the odd quality of self-regulating against anticompetitive forces.

Then again, just because that’s how history has been read at this point doesn’t mean it is certain to continue in that pattern, which leaves the FTC with the task of deciding whether or not Facebook’s gobbling up of an alleged competitor really is anticompetitive; or, if so, if it is anticompetitive enough that it will even still be a relevant acquisition a few years for now.

This article has been updated to reflect the following correction: an earlier version stated that it was the Federal Trade Commission that blocked the AT&T/T-Mobile merger. It was in fact the Department of Justice.